How to hack for VGM files?

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cosbyshow
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How to hack for VGM files?

Post by cosbyshow »

Hello. I'm new :)

I'm hoping someone can help me since I'm new to how all this hacking works, and I can't find any topics on this board that have discussed it. Basically, I'm aware that generally you rip VGMs by logging the sound through Kega. What I want to do though is be able to find any music that might be hidden inside of some games that have gone unused. I noticed there's several games that have an unused track or two included in the VGM packs here, I just want to know how exactly you go about getting those out? I'm assuming it involves hacking the value of the song playing at a certain point so that it's playing a different track, or something like that.

As an example I saw an earlier thread on this board mention a topic on Sonic Retro where someone said Micheal Jackson's Beat It was hidden inside the Dynamite Headdy beta. I'm surprised no one that even knows how to do this has gone and tried to get that out as a VGM yet.

I'd very much like it if someone could just explain how this is done. Thanks :)
SmartOne
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Post by SmartOne »

Let me know if you ever find out. :p
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Dark Pulse
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Post by Dark Pulse »

Usually hacking a game in this manner requires you know either Z80 assembly, or else find the right "byte" to edit in a game's savestate so you can get it to play whatever song you want.

Unfortunately, this address varies from game to game, sound engine to sound engine, and savestate to savestate - what works for one will not work for another.

Squarewave tended to run games through MESS and/or HazeMD to find these addresses, but I don't know the exact method or methods he used.

I'll see if maybe I can get him in here for a rare appearence to answer this.
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MIKE-STAMP
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Post by MIKE-STAMP »

When I made my weird Genesis music jukebox with a number of z80 sound engines put into the same cart I found the 68K->z80 control locations by setting all the z80 memory to 0 (editing save states) then looking for addresses that where changed by the 68000, I put 8 games music in my jukebox... I was bored. I seem to remember most emulators use the genecyst save state format.
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